Scientists have formed numerous different polyhydroxylated molecules. Carbon-based systems are well-known. For example, carbohydrates are ubiquitous in nature and serve as a source for chemical energy (glucose), the backbone for genetic information (ribose), and the organic constituents of plants (cellulose) or insects (chitin) (D. Voet, J. G. Voet, Biochemistry, 2nd ed., Wiley, New York, 1995, pp. 251-276. The three-dimensional network of silica and its derived minerals (F. Liebau, Structural Chemistry of Silicates, Springer, New York, 1985, p. 4) results from the condensation of polyhydroxylated silicates.
However, very few polyhydroxylated boron compounds are known. The most prominent polyhydroxylated boron compound is boric acid, B(OH)3. Alkaline solutions of B(OH)3 deposit Na2[B4O5(OH)4]xc2x7nH2O, which constitutes two abundant boron minerals, kernite (n=2) and borax (n=8) (F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley, New York, 1988, pp. 164-169.). Other common boron structures include the trigonal and tetrahedral boron-oxygen units common to borate minerals, (G. A. Heller, Top. Curr. Chem. 1986, 131, 39-98), and the icosahedron. The allotropes of elemental boron, (J. Donohue, The Structures of the Elements, Wiley, New York, 1974, pp. 48-82) boron-rich solids (H. Hubert, B. Devouard, L. A. J. Garvie, M. O""Keeffe, P. R. Buseck, W. T. Petuskey, P. F. McMillan, Nature 1998, 391, 376-378) and the parent anion of the polyhedral boranes, [closo-B12H12]2xe2x88x92 First reported by Hawthorne et al (A. R. Pitochalli and M. F. Hawthorne J. Am.Chem. Soc., 1960, 82, 3228 followed by J. A. Wunderlich, W. N. Lipscomb, J. Am. Chem. Soc. 1960, 82, 4427-4428) all contain B12 icosahedral
The charge-delocalized icosahedral ion [closo-B12H12]2xe2x88x92, may be considered as the parent aromatic species for borane chemistry in a manner similar to that served by the benzene ring in organic (carbon) chemistry (M. F. Hawthorne, Advances in Boron Chemistry, Special Publication No. 201, Royal Society of Chemistry, London, 1997, pp. 261-272). However, while certain benzene and other aromatic compounds are known,(ie., phenol, hydroquinone, naphthol) fully hydroxylated aromatic compounds (all xe2x80x94H replaced by xe2x80x94OH) are not known or readily prepared. However, contrary to the process described herein for manufacturing the new hydoxylated borates, no reaction occurs when benzene is refluxed with boiling hydrogen peroxide. Isoelectronic substitution of one or two :Bxe2x80x94H vertices in [closo-B12H12]2xe2x88x92 by :Cxe2x80x94H+ provides the aromatic derivatives [closo-1-CB11H12]xe2x88x92, and a set of three isomeric dicarbacarboranes (1,2- or ortho; 1,7- or meta; and 1,12- or para) closo-C2B10H12 R (N. Grimes, Carboranes, Academic Press, New York, 1970, p. 8). Each of these isoelectronic derivatives of [closo-B12H12]2xe2x88x92, undergoes characteristic hydrogen-substitution reactions at their Bxe2x80x94H vertices resulting in a huge number of known icosahedral species.
Of special interest are derivatives in which every available Bxe2x80x94H vertex has been substituted. Thus, hydrophobic derivatives of [closo-B12H12]2xe2x88x92 and [closo-1-CB11H12]xe2x88x92, and the three isomeric dicarboboranes, such as [closo-B12Cl12]2xe2x88x92 (W. H. Knoth, H. C. Miller, J. C. Sauer, J. H. Balthis, Y. T. Chia, E. L. Muetterties, Inorg, Chem, 1964, 3, 159-167), [closo-CB11(CH3)12]xe2x88x92, (King, B. T.; Janousek, Z.; Grxc3xcner, B.; Trammell, M.; Noll, B. C.; Michl, J. J Am. Chem. Soc. 1996, 118, 10902-10903), closo-1,12-C2B10(CH3)12, (W. Jiang, C. B. Knobler, M. D. Mortimer, M. F. Hawthorne, Angew. Chem. 1995, 107, 1470-1473; Angew. Chem. Int. Ed. Engl. 1995, 34, 1332-1334.) and, [closo-B12(CH3)12]2xe2x88x92 (T. Peymann, C. B. Knobler, M. F. Hawthorne, J.Am. Chem. Soc., 1999, 121, 5601) have been synthesized. However, the existence or formulation of similar highly substituted polyhedral borane derivatives having hydrophilic substituents, such as hydroxyl have not been demonstrated.
It was found that per-B-hydroxylated icosahedral borane derivatives, which may be considered to be derivatives of a new type of polyhedral sub-boric acid, can be readily synthesized. Described herein are the per-B-hydroxylated icosahedral Cs2[closo-B12(OH)12],; Cs[closo-1-H-1-CB11(OH)11]; and closo-1,12-H2-1,12-C2B10(OH)10. These borohydrate compounds are prepared by the oxidation of the icosahedral boranes [closo-B12H12]2xe2x88x92, [closo-1-CB11H12]xe2x88x92 and closo-1,12-(CH2OH)2-1,12-C2B10H10, respectively, with 30%W hydrogen peroxide at the reflux temperature (from about 100xc2x0 C. to 50xc2x0 C.) (Peymann T. etal, Angew, Chem. Ind. Ed, 1999, 38, No.8, 1062-1063)
It has now been found that all of the hydroxyls on per-B-hydroxylated icosahedral boranes can be readily converted to ethers and esters with the general formulas [closo-B12(OCOR)12]2xe2x88x92 and [closo-B12(OCR)12]2xe2x88x92 where R is an alkyl, alkene or alkyne or a benzyl or substituted benzyl group. The esters are prepared by reacting the perhydroxylated compound with an organic anhydride or acid chloride, such as acetic anhydride or benzoyl chloride. The ether is prepared by reacting the perhydroxylated compound with various alkylating agents such as benzyl chloride.